Metaphysical hip prosthesis

ABSTRACT

A hip prosthesis has an oblong plate with at one head end a mounting pin provided with a hinge ball, and at the opposite head end a fastening pin for fastening the hip prosthesis in a shaft of a bone. A first part of the plate extends on a first side of the mounting pin. The mounting pin forms an angle α smaller than 90 degrees with the first part of the plate and the tangent to the fastening pin at the location of the connection between the fastening pin and the first part of the plate forms an angle β greater than 90 degrees with the first part of the plate. In order to insert the hip prosthesis into a bone in a simple manner, the fastening pin includes a curved shape from the plate onwards in a direction to the first part of the plate.

FIELD OF THE INVENTION

The invention relates to a hip prosthesis, and more particularly to a hip prosthesis comprising a mounting pin having a hinge ball and a fastening pin for fastening the hip prosthesis in a shaft of a bone.

BACKGROUND OF THE INVENTION

A hip prosthesis of this type is disclosed in EP-A-1 205 163, which is hereby incorporated by reference in full. In this known hip prosthesis the fastening pin has a cylindrical shape and the fastening pin, after being introduced by surgery, extends along the axis of the neck portion of the bone, the part of the bone at which the ball part of the hip joint was present.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a hip prosthesis which can be fixed in the bone in similar sturdy manner to the known hip prosthesis and with minimum invasive techniques, while the opening for introducing the hip prosthesis can be smaller than when the prior art hip prosthesis is introduced. For this purpose the hip prosthesis according to the invention is characterized in that the fastening pin, seen in longitudinal section, has a curved shape from the abutment surface onwards in a direction to the first part of the abutment surface, while the tangent to the hollow side of the fastening pin at the location of the abutment surface forms an angle β that is greater than 90 degrees with the first part of the abutment surface. As a result of the fastening pin being of a curved nature and shorter than the prior art hip prosthesis, the hip prosthesis according to the invention can be introduced through a smaller opening than the prior art hip prosthesis.

An embodiment of the hip prosthesis according to the invention is characterized in that the angle β is between 100 and 120 degrees. The angle β is preferably equal to 110 degrees.

A further embodiment of the hip prosthesis according to the invention is characterized in that the angle α is between 40 and 70 degrees. The angle α is preferably between 50 and 60 degrees.

A still further embodiment of the hip prosthesis according to the invention is characterized in that the inner radius of curvature of the fastening pin is between 60 and 120 millimeters. The inner radius of curvature of the fastening pin being between 60 and 120 millimeters. The inner radius of curvature of the fastening pin is preferably between 75 and 100 millimeters.

The hip prosthesis according to the invention may be fixed in the bone in both uncemented and cemented fashion. An embodiment of the hip prosthesis according to the invention that is suitable for being fixed in both uncemented and cemented fashion is characterized in that the hip prosthesis preferably comprises an oblong plate which is present between the mounting pin and the fastening pin and runs parallel to the abutment surface, the mounting pin being present at one head end of the plate and the fastening pin being present at the opposite head end, the plate extending along the greater part of the circumference to beyond the fastening pin and forming a flange. The plate can then form one whole with the mounting pin and the fastening pin and can be a separate part and be introduced between mounting pin and fastening pin in detechable fashion or not.

Grooves are then preferably present in the fastening pin, which extend in longitudinal direction of the fastening pin starting from the free end of the fastening pin, while the ends of the grooves at the free end of the fastening pin are open. With uncemented application of the hip prosthesis the advantage of these grooves is that the growing of bone into the fastening pin is improved. With cemented application of the hip prosthesis the bone cement will fill up the grooves when the hip prosthesis is introduced into the shaft filled with bone sement, so that improved fixation is effected.

An embodiment of the hip prosthesis according to the invention, which is notably suitable for being fastened in uncemented fashion, is characterized in that the fastening pin of the hip prosthesis is provided with a foam coating. This coating is preferably in essence a tantalium or titanium coating. As a result, bone can grow into the coating, so that the hip prosthesis is fixed in the bone and peak tensions inside the bone at the location of the free end of the fastening pin are reduced or do not even occur at all.

A further embodiment of the hip prosthesis according to the invention is characterized in that at the location of or in close proximity to the first end the fastening pin is provided with a protruding ridge that extends over the entire circumference of the fastening pin. The advantage of this is that when the hip prosthesis is applied to a bone, a watertight sealing is obtained between the hip prosthesis and the bone at this spot, so that, in case of a bacterial infection, the bacteries are kept away from the bone.

The ridge is preferably provided with a watertight coating, so that an even better sealing is obtained.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be further described below in more detail with reference to embodiments of the hip prosthesis according to the invention represented in the drawing figures, in which:

FIG. 1 shows a first embodiment of the hip prosthesis according to the invention of a plate in longitudinal section;

FIG. 2 shows a perspective view of the hip prosthesis represented in FIG. 1;

FIG. 3 shows a side view of the hip prosthesis represented in FIG. 1; and

FIG. 4 shows a side view of a second, flangeless embodiment of the hip prosthesis according to the invention.

DETAILED DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows a longitudinal section of an embodiment of the hip prosthesis according to the invention. The hip prosthesis 1 has an oblong plate 3 with at one head end a mounting pin 5 for mounting a hinge ball of a hip joint and at the opposite head end a fastening pin 7 for fastening the hip prosthesis in a shaft of a bone. A first part 3A of the plate here extends to a first side of the fastening pin 5 and a second part 3B of the plate extends to a second side of the mounting pin.

The mounting pin 5 forms an angle α smaller than 90 degrees with the first part 3A of the plate and the tangent L1 to the fastening pin 7 at the location of the connection of the fastening pin to the first part 3A of the plate forms an angle β greater than 90 degrees with the first part 3A of the plate. The tangent L2 to the fastening pin 7 at the location of the connection of the fastening pin to the second part 3B of the plate forms an angle γ with the second part 3B which is substantially equal to angle β.

The fastening pin 7 is curved from the plate 3 onwards in a direction to the first part 3A of the plate. Then the fastening pin 7, seen in longitudinal direction, tapers to the free end 7A.

At the location of the first part 3A of the plate, the plate protrudes beyond the fastening pin 7 and at the location of the second part 3B of the plate the end of the plate abuts on the outer wall 7B of the fastening pin. The plate 3, mounting pin 5 and fastening pin 7 are manufactured as one whole.

Preferably there are various embodiments of the hip prosthesis of which the angle α and the inner radius of curvature R of the fastening pin 7 are different from each other. Depending on the shape of the bone in which the hip prosthesis is introduced, there may be chosen for the hip prosthesis that fits best. In all these embodiments the angle α is between 50 and 60 degrees and the radius of curvature R is between 75 and 100 millimeters. In all these embodiments the angle β is equal to 110 degrees.

In FIG. 2 the hip prosthesis 1 is shown in perspective view for clarity. The hip prosthesis 1 can be fixed in the shaft of a bone with both bone cement and in uncemented fashion. The side walls 7C of the fastening pin 7 are provided with grooves 9, so that in the case of cemented fixation the bone cement can better bond to the fastening pin. The grooves extend from the free end 7A in longitudinal direction of the fastening pin 7. At the location of the free end 7A the ends of the grooves 9 are open, so that when the hip prosthesis is inserted into the shaft of the bone the bone cement can flow better into the grooves 9. In FIG. 3, in which a side view is shown of the hip prosthesis 1, it is clearly noticeable that the ends 9A of the grooves 9 are open.

FIG. 4 shows a side view of a second embodiment of the hip prosthesis according to the invention. This hip prosthesis 11 is intended to be inserted without bone cement into the shaft of a bone. The hip prosthesis does not have a plate, at a first end 13A of the the mounting pin 13 there being provided a cone 15 for mounting a hinge ball for a hip joint. The second end 13B of the mounting pin is directly fastened to a first end 17A of the fastening pin 17. This end is provided with an abutment surface 19 of which a first part 19A, seen in side view, extends to a first side of the mounting pin and a second part 19B of the abutment surface extends to a second side of the mounting pin. The mounting pin 13, seen in side view, forms an angle α′ smaller than 90 degrees with the first part 19A of the abutment surface, and the tangent L to the hollow side of the fastening pin at the location of the abutment surface 19 forms and angle β′ greater than 90 degrees with the first part 19A of the abutment surface.

In order to obtain a proper bonding of the hip prosthesis in the bone the surface 17C of the fastening pin 17 has a foam coating made of tantalium or titanium so as to enable bone growth. In the proximity of the first end 17A the fastening pin 17 may have a protruding ridge 21 that is provided with a conventional watertight coating. The advantage of this is that when the hip prosthesis is inserted into a bone a watertight sealing is obtained between the hip prosthesis and the bone at this spot, so that in case of a bacterial infection, the bacteries are kept away from the bone.

Albeit the invention has been elucidated in the foregoing with reference to the drawing figures, it should be set out that the invention is not by any manner or means restricted to the embodiments shown in the drawing figures. The invention also extends to any embodiments deviating from the embodiments shown in the drawing figures within the spirit and scope defined by the claims. For example, the protruding ridge in the embodiment shown in drawing FIG. 4 is not necessary if the fastening pin in lieu of being provided with a non-watertight foam coating is provided with a conventional watertight coating. In that case the ridge may thus be omitted. 

1. A hip prosthesis comprising: a mounting pin having a first end provided with a hinge ball or means for mounting a hinge ball for a hip joint, as well as a fastening pin for fastening the hip prosthesis in a shaft of a bone, which fastening pin has a first end provided with an abutment surface and connected to a second end of the mounting pin, a first part of the abutment surface extending, seen in longitudinal section, on a first side of the mounting pin and a second part of the abutment surface extending on a second side of the mounting pin, the mounting pin, seen in longitudinal section, including an angle α smaller than 90 degrees with the first part of the abutment surface, characterized in that the fastening pin, seen in longitudinal section, has a curved shape from the abutment surface onwards in a direction to the first part of the abutment surface, while the tangent to the hollow side of the fastening pin at the location of the abutment surface forms an angle β that is greater than 90 degrees with the first part of the abutment surface.
 2. A hip prosthesis as claimed in claim 1, characterized in that the angle β is between 100 and 120 degrees.
 3. A hip prosthesis as claimed in claim 1, characterized in that the angle α is between 40 and 70 degrees.
 4. A hip prosthesis as claimed in claim 1, characterized in that the inner radius of curvature of the fastening pin is between 60 and 120 millimeters.
 5. A hip prosthesis as claimed in claim 1, characterized in that the hip prosthesis further comprises an oblong plate which is present between the mounting pin and the fastening pin and runs parallel to the abutment surface, the mounting pin being present at one head end of the plate and the fastening pin being present at the opposite head end of the plate, the plate extending along the greater part of the circumference to beyond the fastening pin and forming a flange.
 6. A hip prosthesis as claimed in claim 1, characterized in that the fastening pin has grooves extending in longitudinal direction of the fastening pin starting from the free end of the fastening pin, while the ends of the grooves at the free end of the fastening pin are open.
 7. A hip prosthesis as claimed in claim 1, characterized in that the fastening pin is provided with a foam coating.
 8. A hip prosthesis as claimed in claim 7, characterized in that the fastening pin is provided with a foam coating.
 9. A hip prosthesis as claimed in claim 8, characterized in that at the location of or in close proximity to the first end the fastening pin is provided with a protruding ridge that extends over the entire circumference of the fastening pin.
 10. A hip prosthesis as claimed in claim 9, characterized in that the ridge is provided with a watertight coating.
 11. A hip prosthesis adapted for attachment to a shaft of a bone, the hip prosthesis comprising: a mounting pin having a first end provided with a hinge ball; and a fastening pin adapted for fastening the hip prosthesis in the shaft of the bone, the fastening pin having a first end and a second end, the first end having an abutment surface, a first part of the abutment surface extending, seen in longitudinal section, on a first side of the mounting pin and a second part of the abutment surface extending on a second side of the mounting pin, the mounting pin, seen in longitudinal section, including an angle α smaller than 90 degrees with the first part of the abutment surface, characterized in that the fastening pin, seen in longitudinal section, has a curved shape from the abutment surface onwards in a direction to the first part of the abutment surface, while the tangent to the hollow side of the fastening pin at the location of the abutment surface forms an angle β that is greater than 90 degrees with the first part of the abutment surface.
 12. A hip prosthesis as claimed in claim 11, characterized in that the angle β is between 100 and 120 degrees.
 13. A hip prosthesis as claimed in claim 11, characterized in that the angle α is between 40 and 70 degrees.
 14. A hip prosthesis as claimed in claim 11, characterized in that the inner radius of curvature of the fastening pin is between 60 and 120 millimeters.
 15. A hip prosthesis as claimed in claim 11, characterized in that the hip prosthesis further comprises an oblong plate which is present between the mounting pin and the fastening pin and runs parallel to the abutment surface, the mounting pin being present at one head end of the plate and the fastening pin being present at the opposite head end of the plate, the plate extending along the greater part of the circumference to beyond the fastening pin and forming a flange. 